The present invention relates to methods of making ceramic aggregate particles. More particularly, the present invention relates to methods of making ceramic aggregate particles comprising ceramic binder, and a plurality of solid particulates. The solid particulates may be abrasive particulates.
A variety of methods of making ceramic aggregate particles, for use in a variety of industries, exist. For example, catalyst pellets used in the hydrogenation of toluene and heptane can be made by combining a metal alloy, a high molecular weight polymer, and optionally a plasticizer (i.e., a transient solvent) into a mixture, forming the mixture into a shape, extracting the plasticizer (e.g., by solvent extraction), calcining the shaped mixture to remove the polymer, and then sintering the shaped mixture to provide catalyst pellets. Additional information can be found in U.S. Pat. Nos. 4,895,994 (Cheng et al.) and 4,900,698 (Lundsager). In the orthopedic and dental industry, hard, shaped, ceramic bodies can be made by melting ceramic binder precursor, cooling the melt, and then crushing the cooled melt to provide ceramic bodies to be used in synthetic bone and dental composition. Additional information can be found in U.S. Pat. No. 5,914,356 (Erbe). In the abrasives industry, ceramic aggregate particles can be made by forming a composition that includes a ceramic binder precursor and a temporary organic binder precursor, placing the composition into a mold, heating the composition in the mold to provide shaped particles, and sintering the shaped particles to bum off the organic binder and provide ceramic aggregate particles. Additional information can be found in U.S. Pat. No. 5,975,988 (Christianson). Other uses for ceramic aggregate particles include, for example, roofing granules, filtration products, hard coatings, shot blast media, tumbling media, brake linings, anti-slip and wear resistant coatings, retro-reflective sheeting and laminate composite structures.
While these conventional techniques are useful, there is always a need for other useful techniques which are less costly, require less labor, require less process space, or require fewer steps than conventional techniques, or, that provide ceramic aggregate particles having similar or improved properties over those made by conventional techniques. For example, techniques for forming ceramic aggregate particles which do not require a molding step may provide a less expensive process. Additionally, techniques which do not require the use of solvents (e.g., toluene or heptane) may be desirable.
A need also exists for a method to produce ceramic aggregate particles which have relatively consistent shapes and sizes in order to provide greater consistency of performance to articles made with such ceramic aggregate particles. Regarding particularly abrasive articles, for example, there continues to be a need for abrasive particles which can provide abrasive surfaces with sustained consistent cut rates for, preferably, extended life times, with consistent work piece finish.
The present invention provides methods of making ceramic aggregate particles. One method according to the present invention comprises:
forming a plurality of ceramic aggregate precursor particles from a composition comprising curable binder precursor material, and ceramic binder precursor material, and a plurality of solid particulates, by forcing the composition through a perforated substrate;
at least partially curing the ceramic aggregate precursor particles;
separating the aggregate precursor particles from the perforated substrate; and
heating the ceramic aggregate precursor particles to provide ceramic aggregate particles, wherein the solid particulates are bonded together by the ceramic binder
In one aspect, the present invention may further comprise the step of combining at least a portion of the ceramic aggregate particles with abrasive article binder material and abrasive material to provide an abrasive article. Alternatively, at least a portion of the ceramic aggregate particles comprise abrasive particles.
Typically, the composition is essentially free of solvent. In one embodiment of methods according to the present invention, the mixture of components may further comprise a plurality of solid particulates. The plurality of solid particulates typically have an average particle size in the range from about 0.5 micrometers to about 1500 micrometers. Typically, the mixture of components further comprises photoinitiator. In one embodiment, the at least partially curing step may comprise thermal curing, radiation curing, or combinations thereof. During the heating step, heating is typically conducted at a temperature in the range from about 500xc2x0 C. to about 1500xc2x0 C.
As used herein, the expression xe2x80x9ccurable binder precursor materialxe2x80x9d refers to any material that is deformable or can be made to be deformed by heat or pressure or both and can be at least partially cured to provide material, such as, for example, ceramic aggregate precursor particles, that are handleable and collectable. As used herein with respect to curable binder precursor material, the expression xe2x80x9cat least partially curedxe2x80x9d means xe2x80x9cpartxe2x80x9d or xe2x80x9callxe2x80x9d of the curable binder precursor material has been cured to such a degree that it is handleable and collectable. The expression xe2x80x9cat least partially curedxe2x80x9d does not mean that part or all of the curable binder precursor is always fully cured, but that it is sufficiently cured, after being at least partially cured, to be handleable and collectable.
As used herein, the expression xe2x80x9chandleable and collectablexe2x80x9d refers to material that will not substantially flow or experience a substantial change in shape. Ceramic aggregate precursor particles and ceramic aggregate particles that are handleable and collectable tend to remain intact if subjected to an applied force that tends to strain or deform a body. Ceramic aggregate precursor particles and ceramic aggregate particles that are not handleable and collectable tend not to remain intact if subjected to an applied force that tends to strain or deform a body.
As used herein, the expression xe2x80x9cceramic binder precursor materialxe2x80x9d refers to particulate additives which, when heated to a temperature sufficient to bum out organic materials present in the ceramic aggregate precursor particle, may subsequently bond together to form a rigid ceramic phase bonding the ceramic aggregate particle together and to provide a ceramic aggregate particle. Ceramic binder precursor material may include crystalline or non-crystalline ceramic material. Hereinafter, xe2x80x9cceramic aggregate precursor particlexe2x80x9d means the ceramic binder precursor material has not yet bonded together sufficiently to provide a particle that is handleable and collectable. Hereinafter, xe2x80x9cceramic aggregate particlexe2x80x9d means the ceramic binder precursor material has sufficiently bonded together to provide a particle that is handleable and collectable. Typically, methods according to the present invention provide at least a portion of the ceramic aggregate particles having an aspect ratio greater than one.
As used herein, the word xe2x80x9cceramicxe2x80x9d means inorganic, non-metallic material that may include a crystalline phase, a noncrystalline phase (e.g., glass), or a combination of both a crystalline phase and a non-crystalline phase (e.g., porcelain, glass-ceramic).
Hereinafter, xe2x80x9cessentially free of solventsxe2x80x9d means the composition used to make ceramic aggregate precursor particles contains less than 10% solvent.
Ceramic aggregate particles made by the present invention can be used in products such as, for example, abrasives, roofing granules, filtration products, hard coatings, shot blast media, tumbling media, brake linings, anti-slip and wear resistant coatings, synthetic bone, dental compositions, retro-reflective sheeting and laminate composite structures.
In one embodiment, methods according to the present invention involve combining at least a portion of the cured ceramic aggregate particles with abrasive article binder material and abrasive material to provide an abrasive article. Suitable abrasive articles include coated abrasive articles (including nonwoven abrasive articles) and bonded abrasive articles.
The method of the present invention provides ceramic aggregate particles where a major portion of the particles have a substantially uniform cross-sectional shape. By xe2x80x9cmajor portionxe2x80x9d it is meant that at least 50 percent, preferably about 90 percent, of the particles have a substantially uniform cross-sectional shape. Such uniform particles provide articles into which they are incorporated with more consistent performance characteristics. For example, abrasive ceramic aggregate made according to the present invention have consistently high cut rates and consistent surface finish for longer life times than do abrasive aggregates prepared by conventional methods.
The method of forming the aggregates of the invention described above are generally less costly, and require fewer steps, and less space and labor than conventional means of making ceramic aggregate particles, such as molding.
The ceramic aggregates produced by the methods of this invention are described in Applicant""s U.S. Ser. No. 09/971,899 (filed on the same date as this application and incorporated herein).